orderedDict 保持元素插入时的顺序
from collections import OrderedDict
d = OrderedDict()
d['foo'] = 1
d['bar'] = 2
d['spam'] = 3
d['grok'] = 4
Outputs "foo 1", "bar 2", "spam 3", "grok 4"
for key in d:
print(key, d[key])
from collections import OrderedDict
d = OrderedDict()
d['foo'] = 1
d['bar'] = 2
d['spam'] = 3
d['grok'] = 4
for key in d:
print(key, d[key])